Research On Key Technologies Of VoIP And The Implement Of Endpoint Model

With the development of network and speech coding technology, the application of transmitting voice over internet protocol (VoIP) network has been came true. By means of using VoIP technology, voice data has been compressed with some coder algorithm, then the compressed data has been transmitted through packed switching network, thus voice communication has been realized. Not only can VoIP technology provide all the services the traditional circuit switching network could gave us, but also can it give us a lot of other new services, all the services VoIP gave us are inexpensive. Holding the advantages of less cost, power function, and easily to be realized, VoIP technology is sure to replace the traditional communication methods. With more than ten years development, VoIP is widely used now. In our country, telecommunication operation is under the control of government, for some reason, the application of VoIP technology has been allowed only in given fields. On the other hand, according to the promise our country gave when join WTO, trade in the basic telecommunication business should be allowed to the foreign capital after six years, and this year is the last limit year. There will be a fierce market competition in telecommunication operation before long. And the contention between VoIP business will be the focus. Now, the emphasis we should study is how to win the advantage over the contention.Under this background, the actual state and the developmental trend of VoIP has been discussed in the paper. The key technologies used in VoIP have been presented. Now days, there are mainly two call signalling protocol used widely, one is H.323 and the other is SIP. The advantage of these two signalling protocol in different field have been discussed. The paper analyzed the structure of a end point used in VoIP, analyzed the function of each part. For the purposes of reduce cost of a end point, a method that cut down the chip used in end point has been presented. If the master chip can complete the works used to be done by a DSP chip, then the DSP chip is needless. The approach is based on reduce the complexity of algorithm should been finished in DSP chip. Technologies of reduce complexity of G729a has been discussed with emphasis. These optimum technologies are based on C language, they are great efficient and can be transplant to other chips easily. The efficiency and the exactitude has been demonstrate by implement G.729a algorithm on EPSONslc33209 and on TMS320vc5402. This paper also discussed another key technology used in VoIP, which is VAD(voice activity detection). On the basis of short time energy and short time cross zero rate, a simple VAD model on G.729 has been presented. The model can adapt to different environments automatically by modify correlative parameters. Experimental results showed that the model is effective and in different voice environments it showed better adaptability.